The present invention relates to cleaning and removing ash deposits from boilers and, more particularly, to generating controllable pressure waves by intermittent combustion and directing the pressure waves at the ash deposits for removal.
During the operation of fossil fuel-fired boilers, especially, coal-fired boilers, the combustion process produces ash. Large boilers used in power generation plants and other industrial and commercial applications can produce especially large amounts of ash. The ash builds up on the heat exchanger tubes inside the boiler, which significantly reduces the heat transfer to the tubes and the thermal efficiency of the boiler. To maintain the desired efficiency of the boilers, boiler designers often install soot blowers which use media such as air or steam to clean specific areas of the boilers. However, in order to remove hard-to-clean deposits and/or deposits from not easily accessible areas of the boilers, operators often have to lower the load or capacity of the boiler and sometimes shut down the boiler. For example, electric utility companies sometimes schedule lowering of loads (derating) every night and/or schedule shutting down the boiler completely every few months or so, each shutdown typically lasting for a couple of days or so, to remove the ash deposits that have built up since the last shutdown. During the periods of derating, and shutdown of the boiler, the lost amount of electricity has to be purchased or obtained from other sources usually at higher prices.
A number of techniques have been developed to remove ash deposits from boilers. One technique involves using retractable water, steam, or air jet equipment to attempt to spray and remove the ash deposits off of the heat exchanger tubes. The thermal shock of the cooler water or other media can produce thermal stresses on the very hot metal heat exchanger tubes resulting in potential cracking and failures, and additional shutdowns for repairs. Another technique involves using shotguns, dynamite, or other explosives to attempt to jar the ash loose from the heat exchangers. But this technique can potentially damage the boiler and further, the boiler has to be shut down to insert the dynamite. And in yet another known technique, compressed air acoustic generators and pulse combustors are used to set up a standing acoustic wave to attempt to jolt the ash off the heat exchangers. But this approach has limited effectiveness because sound waves dissipate quickly and the loudness and frequencies needed to effectively remove the ash are harmful or at least very aggravating to the human ear.
Accordingly, what is needed but not found in the prior art is a way to remove ash deposits from boilers in order to maintain a high availability and high thermal efficiency. In particular, there is a need for a system and method for removing the existing ash deposits while the boiler is being operated and for not allowing ash deposits to build up excessively any further on the heat exchangers, and thus minimizing any derating and loss of availability of the boiler. Furthermore, there is a need for such a system and method that is time- and cost-effective to build, install, operate, and maintain. It is to the provision of such an ash deposit removal system and method that the present invention is primarily directed.
The present invention is an impulse system for removing deposits such as ash from heat exchangers or other surfaces in a boiler or other apparatus. Generally described, the impulse system includes at least one impulse generator and a control system operably connected to the impulse generator. The impulse generator has a hollow body and an ignitor. The hollow body has an inlet for air, an inlet for fuel, and an outlet for ignited air and fuel, with the outlet connected to the boiler. The control system is operable to activate the ignitor to ignite the air and fuel in the impulse generator body. The ignition of the air/fuel produces a pressure wave that is directed through the outlet and into the boiler to remove the ash deposits.
The control system includes conventional control components such as a programmable logic controller connected to input sensors and output components. For example, the input sensors may include pressure, temperature, and flow sensors, and the output components may include control valves and ignition timing controls. In this way, the control system is operable to monitor and precisely control the combustion process to generate desired pressure oscillations and the resulting pressure waves.
Preferably, the control system is operable to adjust the fuel flow, air flow, ignition dwell time (duration of spark), or ignition interval time (time between sparks), or a combination of these. In this way, the impulse generator can be controlled to produce high-pressure detonative combustion, intermediate-pressure deflagrative combustion, low-pressure pulse combustion, or a combustion process in the transition zones between these. The preferred combustion mode is a function of the properties of the deposit to be removed. So the control system permits adjusting the combustion mode to match the most efficient or effective mode for the deposit that is present.
In addition, the impulse generator is preferably configured to induce a helical swirling flow of the fuel and the air. This enhances air/fuel mixing for a more complete and uniform combustion, which is more fuel-efficient and controllable.
In a first exemplary embodiment of the present invention, the impulse generator hollow body is generally toroidal-shaped, forming a looped air and fuel flow path. The air inlet is preferably generally tangential to a plan view flow path centerline of the body. This induces the fuel and the air to flow in a loop around and around within the body. In addition, the air inlet is preferably generally tangential to a side view cross section of the body for inducing the helical swirling flow of the fuel and the air in the body.
The outlet is positioned to discourage the helically swirling air and fuel from leaking into the boiler before it is ignited. For example, the outlet can be perpendicular to a side view centerline of the impulse generator body and flared. In this way, the helically swirling air and fuel will tend to flow past the outlet and continue flowing around in the impulse generator body until ignited by an ignition source.
In alternatives to the first embodiment, the body is spiral-shaped, has a 270 degree turn, has a combined air/fuel inlet for use with a pre-mixer, has an acutely angled air inlet for further inducing the helical swirling flow, has a tangential outlet in an opposite direction from the helically swirling air/fuel, and/or has a corkscrew-shaped vane. Those skilled in the art will understand that other alternative embodiments can be used to accomplish the desired ash deposit removal.
In a second exemplary embodiment of the present invention, the impulse generator includes a turbulizer including at least one vane for inducing the helical swirling flow of the fuel and air. For example, the vane can be generally corkscrew-shaped and positioned in the impulse generator body. And the fuel inlet conduit can be extended into the body, provided with fuel apertures, and have the vane formed on it. In this way, the fuel flows through the fuel conduit and out through the apertures so that it is dispersed evenly into the body where it is induced into the helical swirling motion with the air as they flow along the vane. Preferably, the hollow body is generally cylindrical and the fuel conduit and air conduit are coaxially arranged.
In a third exemplary embodiment of the present invention, the impulse generator includes a turbulizer with at least one vane configured for use with a combined air/fuel inlet and, preferably, a pre-mixer. In this embodiment, the shape, size, number, and spacing of the vane ridges, as well as the position of the ignitor, can be modified from the second embodiment in order to induce continuation of the helical swirling flow of the fuel and air after ignition.
Additionally, the present invention provides an exemplary method for removing ash or other deposits from a boiler or other apparatus. The method includes the steps of providing at least one impulse generator in communication with the boiler, introducing air and fuel into the impulse generator, and igniting the air and fuel to produce pressure waves that are transmitted from the impulse generator into the boiler to remove the ash deposits from the boiler.
The method preferably includes the steps of inducing a helical swirling flow of the fuel and the air in the impulse generator. This can be facilitated by providing the impulse generator with a toroidal-shaped body similar to that of the first embodiment, a turbulizer with at least one cork-screw-shaped vane similar to those of the second or third embodiment, or a combination of these.
In addition, the ash deposit removal method preferably includes a combustion mode adjustment process. This adjustment method includes the step of selecting a combustion mode based on certain properties of the ash deposit. Such properties may include the distance of the deposit from the impulse generator outlet, whether the deposit is encrusted or fused to the surface to be cleaned, the weight and density of the deposits, etc. Different combustion modes are desirable for removing different types of these deposits. Different combustion modes include, for example, detonative combustion for generating a higher pressure, deflagrative combustion for generating an intermediate pressure, and pulse combustion for generating a lower pressure.
The adjustment method further includes the step of adjusting the control system for the impulse generator to produce the selected combustion mode. This adjustment can be made by adjusting the fuel flow, air flow, ignition dwell time, ignition interval time, or a combination of these. By selectively controlling the combustion mode of the impulse generator in this way, the impulse system can be operated most efficiently and effectively to maximize the operational efficiency of the boiler.
In view of the foregoing, it will be appreciated that the present invention provides for removing ash deposits from heat exchangers in a boiler while it is running. So the boiler does not need to be shut down for the cleaning and ash deposits do not build up so much. In this way, the boiler is kept in much better operating condition and operates at a consistent and relatively high thermal efficiency. Furthermore, the present invention is time- and cost-effective to implement.